In a delayed coking process, overhead vapors from a coke drum are passed to a coke fractionator wherein the coker overheads are separated into a vapor stream, one or more intermediate liquid streams, and a flash zone gas oil (FZGO) stream. The FZGO stream often contains significant amounts of finely divided particulate solids (e.g. coke fines) of varying diameter, as well as heavy viscous mesophase material. The mesophase material can be liquid coke that is entrained in the vapors leaving a coke drum and is often coated on coke particles, making the particles sticky. In order to enhance the value of an FZGO stream, further processing is necessary, and it is desirable to pass the FZGO stream to, for example, a fixed bed catalytic hydroprocessing unit and then to a fluidized bed catalytic cracking (FCC) unit or to other processing units. Undesirably, however, entrained solids and mesophase material in the FZGO stream can quickly plug and foul the catalyst bed of the hydroprocessor.
Unhydrotreated flash zone gas oil can be processed in a fluidized bed catalytic cracking unit (FCC unit), but the yield distribution of the unhydrotreated FZGO stream is generally poor due to its highly aromatic content and other factors.
A filter medium can be used to filter out particles from the FZGO stream. However, filtration processes are susceptible to filter plugging, can require significant periods of shutdown to clean or remove tar or gum build up to regenerate the filter medium, and can require significant initial capital expenditure to install.
It would be advantageous, therefore, to provide a process and an apparatus that operate efficiently and economically to remove particulate material from the FZGO stream, thereby facilitating subsequent processing of the FZGO stream and providing an opportunity for improving refinery economics by enhancing the value of the FZGO stream.